content: /**
   * Copyright (c) 2016-present, RxJava Contributors.
   *
   * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in
   * compliance with the License. You may obtain a copy of the License at
   *
   * http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software distributed under the License is
   * distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See
   * the License for the specific language governing permissions and limitations under the License.
   */
  
  package io.reactivex.interop.internal.operators;
  
  import org.reactivestreams.*;
  
  import hu.akarnokd.reactivestreams.extensions.RelaxedSubscriber;
  import io.reactivex.common.Disposable;
  import io.reactivex.common.exceptions.Exceptions;
  import io.reactivex.common.functions.BiFunction;
  import io.reactivex.common.internal.functions.ObjectHelper;
  import io.reactivex.flowable.internal.subscriptions.SubscriptionHelper;
  import io.reactivex.observable.*;
  
  /**
   * Reduce a sequence of values, starting from a seed value and by using
   * an accumulator function and return the last accumulated value.
   *
   * @param <T> the source value type
   * @param <R> the accumulated result type
   */
  public final class FlowableReduceSeedSingle<T, R> extends Single<R> {
  
      final Publisher<T> source;
  
      final R seed;
  
      final BiFunction<R, ? super T, R> reducer;
  
      public FlowableReduceSeedSingle(Publisher<T> source, R seed, BiFunction<R, ? super T, R> reducer) {
          this.source = source;
          this.seed = seed;
          this.reducer = reducer;
      }
  
      @Override
      protected void subscribeActual(SingleObserver<? super R> observer) {
          source.subscribe(new ReduceSeedObserver<T, R>(observer, reducer, seed));
      }
  
      static final class ReduceSeedObserver<T, R> implements RelaxedSubscriber<T>, Disposable {
  
          final SingleObserver<? super R> actual;
  
          final BiFunction<R, ? super T, R> reducer;
  
          R value;
  
          Subscription s;
  
          ReduceSeedObserver(SingleObserver<? super R> actual, BiFunction<R, ? super T, R> reducer, R value) {
              this.actual = actual;
              this.value = value;
              this.reducer = reducer;
          }
  
          @Override
          public void onSubscribe(Subscription s) {
              if (SubscriptionHelper.validate(this.s, s)) {
                  this.s = s;
  
                  actual.onSubscribe(this);
  
                  s.request(Long.MAX_VALUE);
              }
          }
  
          @Override
          public void onNext(T value) {
              R v = this.value;
              try {
                  this.value = ObjectHelper.requireNonNull(reducer.apply(v, value), "The reducer returned a null value");
              } catch (Throwable ex) {
                  Exceptions.throwIfFatal(ex);
                  s.cancel();
                  onError(ex);
              }
          }
  
          @Override
          public void onError(Throwable e) {
              value = null;
              s = SubscriptionHelper.CANCELLED;
              actual.onError(e);
          }
  
          @Override
          public void onComplete() {
              R v = value;
              value = null;
              s = SubscriptionHelper.CANCELLED;
              actual.onSuccess(v);
          }
  
          @Override
          public void dispose() {
              s.cancel();
              s = SubscriptionHelper.CANCELLED;
          }
  
          @Override
          public boolean isDisposed() {
              return s == SubscriptionHelper.CANCELLED;
          }
      }
  }
  